System-Level Fault Tolerance (Clustering/Network Load Balancing) - Shared Storage Devices
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Shared disk storage was a requirement for all previous releases of MSCS until Windows Server 2003. Now only the traditional design of a single quorum device cluster has such a requirement, but a shared storage device can be a part of any cluster configuration.
In the past, storage area networks (SANs) were used to satisfy the shared storage device requirement. The logical volumes created in the SAN device must be configured and recognized as basic disks by the Windows Server 2003 operating system. Windows Server 2003 identifies the logical volumes on the SAN by their disk signatures, and each volume is treated as a separate disk by MSCS. Currently, dynamic disks are not supported for shared disk volumes. SCSI SAN units are supported on two-node clusters, but for clusters with more than two nodes, fiber channel is the preferred method of connecting cluster nodes to the shared storage.
Using a single fiber channel, Windows Server 2003 can access both shared and nonshared disks residing on a SAN. This allows both the shared storage and operating system volumes to be located on the SAN, giving administrators the flexibility of deploying diskless servers. Of course, the SAN must support this option, and the boot drives must be assigned exclusive access for individual cluster nodes through proper disk zoning and masking. Consult SAN vendor documentation and check the Cluster HCL on the Microsoft Web site to find approved SAN devices.
The Cluster server uses a shared nothing architecture, which means that each cluster resource can be running on only one node in the cluster at a time. When a disk resource is failed over between nodes, the SAN device must be reset to accommodate the mounting of the disk on the remaining node. If the SAN device is used by more than just cluster nodes, SAN communication can be disrupted to other servers if the SAN is not configured to reset only the targeted logical unit number (LUN) as opposed to resetting the entire bus. Windows Server 2003 supports targeted LUN resets, and SAN vendor documentation should be reviewed to ensure proper zoning and masking of the SAN device.
Multipath I/O
Windows Server 2003 supports multipath I/O to external storage devices such as SANs. This allows for multiple redundant paths to external storage, adding yet another level of fault tolerance. This capability is now achieved through redundant fiber channel controller cards in each cluster node.
Volume Shadow Copy for Shared Storage Volume
The Volume Shadow Copy (VSS) service is supported on shared storage volumes. Volume Shadow Copy can take a point-in-time snapshot of an entire volume, enabling administrators and users to recover data from a previous version. The amount of disk space used for each copy can be minimal, so enabling the service can add data fault tolerance and reduce recovery time of a file or folder. Volume Shadow Copy should be tested thoroughly on a disk containing enterprise databases such as Microsoft SQL 2000 prior to implementation to ensure that it can provide fault tolerance and recoverability as required and to ensure that databases do not suffer corruption as a result of a rollback to a previous version of the database file.
Single-Quorum Cluster Scalability
The single-quorum cluster is composed of independent server nodes that all connect to a share's storage device such as a SAN. Table 31.1 specifies the minimum and maximum number of nodes and types of storage communications allowed in a single-quorum cluster.
Table 31.1 Number of Nodes Allowed in a Cluster
Operating System | Number of Nodes | Allowed Cluster Storage Device |
Windows Server 2003 Enterprise Server | 2, 3, 4, 5, 6, 7, or 8 | SCSI, fiber channel (recommended for clusters with more than two nodes) |
Windows Server 2003 Datacenter Edition | 2, 3, 4, 5, 6, 7, or 8 | SCSI, fiber channel (recommended for clusters with more than two nodes) |
64-bit edition of Windows Server 2003 Enterprise Server | 2, 3, 4, 5, 6, 7, or 8 | Fiber channel |
64-bit edition of Windows Server 2003 Datacenter Edition | 2, 3, 4, 5, 6, 7, or 8 | Fiber channel |
 This chapter is from Microsoft Windows Server 2003 Unleashed, by Rand Morimoto, et al. (Sams Publishing, 2004, ISBN: 0672326671). Check it out at your favorite bookstore today.
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